A network system, e.g. a local area network as shown in FIG. 1, consists of a plurality of stations 101˜105 and a hub 10 connected to the stations 101˜105. The stations 101˜105 can be personal computers or computer servers, which transfer/receive data packets to/from one another via the hub 10. As a hub is substantially a Level 1 device, it merely functions for connection of stations other than management of data packets. In other words, the stations may arbitrarily transfer data via the hub by sharing the bandwidth. The more the stations work through the hub, the slower the operational speed of the network system due to the limitation of bandwidth.
Switch hubs which are Level 2 devices are thus developed for transferring and managing data packets among stations in order to maintain the operational speed of the network system at a satisfactory level. A switch hub not only allows data packets to be transferred thereby but also functions for screening data packets and allocating the data packets.
A switch hub and its operational principle are illustrated in FIG. 2A and FIG. 2B. For example, the switch hub 2 is connected thereto a first station 201 and a second station 202. The switch hub 2 includes a controlling and processing unit 20, a switch device 21, a buffer 22 and a storage unit 23. When the first station 201 is to transfer a data packet to the second station 202 via the switch hub 2, the controlling and processing unit 20 checks the contents from Level 2 to Level 7 (L2˜L7 contents) of the data packet to classify the data packet. If there is space available in the buffer 22 to receive the coming data packet, the data packet will be stored into the buffer 22 after being classified according to its L2˜L7 contents and wait to be transmitted to a destination station, e.g. the station 202. The destination station is determined according to a destination address recorded in the transmitted data packet and an address correlation table 231 stored in the storage unit 23. On the other hand, when the buffer 22 has no further space for the coming data packet, the controlling and processing unit 20 corresponds the L2˜L7 contents to a specified action according to a classifying table, which is briefly depicted in FIG. 2B. For example, when the L2˜L7 contents 0 indicates that the data packet is a transmission control protocol (TCP) packet, the action 0 can be a retransmit action when the buffer 22 has no further space for the coming data packet. That is, the TCP data packet is requested to issue a retransmit signal to the station 201 via the controlling and processing unit 20 and the switch device 21 in order to have the data packet successfully transmitted. In another example, when the L2˜L7 contents 1 indicates that the data packet is a user datagram protocol (UDP) packet, the action 1 can be a discard (not retransmit) action when the buffer 22 has no further space for the coming data packet.
An example of the UDP data is video/audio data transmitted for a video conference in a local area network. The transmission of such data is required to be real time and the data is not allowed to be retransmitted. If the video conference is being held while the there are a number of data packets being transmitted in the network, the buffer 22 is likely to become full soon, particularly when there are many data being transmitted and repetitively retransmitted. In the mean time, the UDP data that are supposed not to be retransmitted may be discarded to an unacceptable degree, resulting in intermittent images and voices.